1. Field of the Invention
The present invention relates to a lens barrel which is preferable with respect to thinning a camera body of a camera provided with a shifting lens holding cylinder such as a collapsible barrel type camera.
2. Related Background Art
By collapsing and containing a lens barrel in a camera body, a camera can be thinned when not used. The shifting amount of the lens barrel, however, can not be made greater than the thickness of the camera body. Accordingly, there has been known a camera whole lens barrel is collapsed by two stages in order to further thin the camera body.
FIG. 5 shows a longitudinal section of a conventional lens barrel of zoom lens of two groups type.
In this lens barrel, a gear 106 is provided around the periphery of an intermediate helicoid 106. When torque from a gear 108 connected with a drive motor is transmitted to the gear 106a, the intermediate helicoid 106 is shifted forward and backward according to the lead of a fixed cylinder 107, and at the same time, a lens holding cylinder 105 which holds a photographing lens 101 is shifted forward and backward according to the lead of the intermediate helicoid 106.
In the above-mentioned conventional lens barrel, however, as the shifting amount of the intermediate helicoid 106 in the direction of the optical axis increases, the gear length A of the gear 106a has to be made longer in order to meet the increased shifting amount.
Therefore, if the shifting amount of the intermediate helicoid is increased too much on purpose to thin the camera body without changing the rest of the constitution, the gear 106a can not be contained in the camera body. So, the camera body can not be thinned very much only by increasing the shifting amount of the intermediate helicoid 106 even when the lens barrel is collapsed by two stages.